A developing device is provided in an image forming apparatus and develops an electrostatic latent image formed on a photosensitive member. The developing device includes a toner storage chamber in which toner is stored, a supply roller that is disposed below the toner storage chamber, a developing roller that is rotatable in a rotational direction while being in contact with a photosensitive member and the supply roller, and a layer thinning blade that is in contact with the outer peripheral surface of the developing roller over an axial direction of the developing roller.
The layer thinning blade is made of elastic metal and has a plate shape. The layer thinning blade includes a base end that is supported by a case of the developing device, and a tip end that is provided upstream of the base end in the rotational direction of the developing roller. The tip end of the layer thinning blade has a bent portion that is bent at a predetermined radius of curvature to be separated from the surface of the developing roller toward the edge of the tip end of the layer thinning blade. The bent portion of the layer thinning blade is in contact with the surface of the developing roller.
In the developing device, the toner stored in the toner storage chamber drops on the supply roller and is then supplied to the surface of the developing roller by the supply roller. The developing roller rotates in the predetermined direction, conveys the toner, which is supplied to the surface of the developing roller, to a contact position where the developing roller is in contact with the bent portion of the layer thinning blade, and then conveys the toner to a contact position where the developing roller is in contact with the photosensitive member. Accordingly, toner is supplied to an electrostatic latent image, which is formed on the photosensitive member, at the contact position where the developing roller is in contact with the photosensitive member, so that the electrostatic latent image is visualized into a toner image.
Here, when the toner, which is supplied to the surface of the developing roller, passes through the contact position where the developing roller is in contact with the bent portion of the layer thinning blade, the thickness of the toner is regulated by the layer thinning blade. Accordingly, a thin toner layer is formed and held on the surface of the developing roller. As the thickness of the toner is regulated by the layer thinning blade, the toner is accumulated on the upstream side (hereinafter, simply referred to as an “upstream side of the bent portion”) of the bent portion in the rotational direction of the developing roller.
Since the toner is accumulated on the upstream side of the bent portion, a stable amount of toner passes through the contact position where the developing roller is in contact with the bent portion of the layer thinning blade. Accordingly, after passing through the contact position where the developing roller is in contact with the bent portion of the layer thinning blade, an inappropriately thin portion can be reduced or prevented from being formed in the thin toner layer that is held on the surface of the developing roller. Accordingly, it is possible to achieve a solid print without a scratched portion.
However, in the above-described developing device, a toner density in the toner image based on the thin toner layer formed through the layer thinning blade on the surface of the developing roller can vary, so that a so called ghost is generated.